Trying to get your Matrox Parhelia card to work with Linux 2.6?
This patch should help. It mostly fixed things for me and I worked relatively happily with my Matrox Parhelia "P650" for about seven months. A few bugs remain -- eg quitting X renders the console unusable. My advice, though, would be to give up now, sell the card, buy a card from nVidia or ATI instead.
The reason for this is simple: Matrox don't give a damn about their Linux customers. At the time of writing the last driver update was over a year ago. Their binary-only driver is buggy, and they refuse to provide direct support for it -- they rely instead on the community to provide support. But they won't in turn support that community. They've released no documentation and updates are released at a truly glacial rate, with no indication of when the next update can be expected or what issues it will address. There are no drivers for non-i386 platforms -- anyone on Athlon64 (in 64-bit mode), PowerPC, ARM or any of the other exotic platforms Linux supports is out in the cold.
About 100 people a month have downloaded this driver patch since I posted it -- and those are just the people who investigated deep enough to find the patch (it's not easy to find!) and then knew what to do with it when they found it. For these people I leave my patch available. But the patch still has problems (eg, the console is unusable after quitting X on my machine) and they will only get worse as the Linux kernel deviates further from the one Matrox originally wrote their code for.
I've thrown my P650 away now. Not sold it, just chucked it out. I couldn't bring myself to lumber some poor sucker with that card. The card itself appears well built and the hardware has the ability to work very nicely, but the software drivers suck and blow at the same time.
Still want to give it a go? Download the patch here, you crazy person!
August 2008 Update
If you're really into supporting free software, go buy an ATI card. ATI (now part of AMD) appear to be committed to releasing documentation to enable the community to write and maintain high-quality open source drivers ... although this is a reasonably big effort that has only just got started.
If you want good drivers right now, and can live with them being proprietary, I suggest you go buy a recent nVidia card. They have good binary drivers and there are good tools from Debian for packaging the binary-only drivers.